I auditioned the B&O system at a dealer before getting my car. I considered ordering and wanted to know if it was worth the extra $900. At first I concluded that it wasn’t. And my opinion was unchanged until now. The bass was way bloated and I couldn’t seem to turn it down enough. The sound quality was rough, and there was not a good stereo image.

It’s as if some Ford project manager swooped in just before sign-off and exclaimed, “Where’s the bass?! We gotta crank up the bass or no one will like it!” Well, I don’t like artificially bloated bass. Here is the custom target curve for my high-end home system. There is about 2dB gradual emphasis from high to low frequency.

Regardless I found a nearly fully loaded car and it came with the B&O system. Oh well, I thought, at least it will have a CD player, and subwoofer wiring harness in case I want to replace it. I already knew about snipping the center speaker wire on my 2016 Mustang.

Some of you may have read my thread “Join me in fixing the center speaker issue”. The overall conclusion of that thread (and as confirmed by many others) is that the sound is simply better with NO center speaker playing. And so we have snipped the green wire (positive lead) going to the speaker, near the amp connector.

I read some other threads on what others have done with their systems. Replacing speakers, amps, programming, and so on.

My opinion (even as a lifelong audiophile and professional loudspeaker designer) was that

The door 3-way speakers are pretty good

The center speaker was cheap and providing horrible sound at a nice loud level, and destroyed the stereo imaging

The package shelf speakers were terrible in the 9-speaker (non-B&O) system. They are decent in the B&O system. They play quieter than the front, and so I no longer have to fade most of the sound to the front.

I did not have a subwoofer on my last (9-speaker) car, and it lacked low and middle bass. But the sub plays way too loud on the B&O system.

Even though I have high standards for my home system, I don’t carry those over to car audio. There are too many intangibles such as background noise, reflective cabin acoustics, driver delays, etc. Even worse is the challenge of working on a car system such as getting into tight spaces, every connector is custom, and endless research just to know what I’m working with.

I first removed the subwoofer box, and then the woofer itself. Of course that required the obligatory breaking of plastic parts.

I then verified connector pins and polarity for the two voice coils. This is a very important step to avoid electrical mishaps.

I wanted to know the voice coil DCR because I intended to test with my lab amp, and so I was concerned about the load impedance being too low. Here is the DCR for one coil, indicating it is nominally 4 ohms.

Next I tested the free-air and in-box impedance of the factory woofer. I used a 4” PVC tube I had to lift the woofer up off the clip leads. It was a real struggle to get the leads to stay on the pins. (Refer to my complaint about specialized connectors.)

Here is the impedance graph:
The sharp rise in impedance above 100Hz indicates that the woofer has no copper in the motor. Something that is featured on higher-end woofers. Not a big deal for an active powered woofer that only serves bass duty.

Then I tested the nearfield SPL response of the factory subwoofer, but this was driven by my Crown K1 lab amp. This provided me the response knowing that there is no EQ programmed in anywhere.

OMG, look at the peaked response!

No worries, I thought. Surely Ford will have EQ’d this hump out of the response. Nope! It is still there in the factory amp driven sub.

I then spent quite a bit of time designing a passive EQ network to flatten the response. These graphs show a better bandpass response from 30 – 100Hz, and intentional loss of -12dB so as to reduce its output. Notice that the impedance is unchanged at very low frequency, and is overall higher than original throughout most of the pass band. This makes it easier to drive by the amp.

Unfortunately, four very large value inductors are called for. Two are needed in series simply because of sourcing a large value, and then two pairs are needed because there are two voice coils.

At this point I decided to do what I should have done from the outset – SPL testing inside the car.

As it turns out, the cabin has a suckout at 60Hz. Maybe that is the reason for the 66Hz response peak? Even though there is a large peak, it still does not fully overcome the 60Hz dip (this curve is with the trunk and windows open – I forgot to close those). This graph was with the mid and treble controls all the way down.

Interesting. I have the 9 speaker system. I did a basic RTA on it. No calibrated mic available so I used the internal mic on my ipad (which is compensated for in the RTA). The 9 speaker system takes a dump at 10khz and there is no more high frequencies produced. The B&O must use a different tweeter or the APIM is EQ'd differently. Thanks for sharing this info.

I first wanted to characterize the gain range of the bass control. IOW, what is the dB span between minimum and maximum settings of the bass tone control?

A new challenge is that I cannot inject my favorite audio analyzer signal into the car, because there is no provision for analog audio input. Therefore I had to fall back on CD test signals.

To probe the connector I made some probe pins out of paper clips, and insulated them (refer to previous comment about electrical mishaps).

I connected my DVM to one of the subwoofer cable channels.
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I played a constant 50Hz test tone from the CD and then plotted the 15 voltage steps from changing the tone control from minimum to maximum. Here is the resulting chart with voltages converted to dB and normalized for 0dB at the middle setting:
So each step is less than a dB, and the graph is nearly a straight line. The tone control has a range of +|- 5dB.

I applaud your efforts @GTP but way more than I'd have done for what's likely a minor sound improvement but we've all got our "thing" and sound quality is obviously yours.

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Yes, you make the obvious and valid point. I.e. that I had to go through all this (from the POV of loudspeaker expert) just to determine that the B&O system is pretty good, but the subwoofer level was set way too high at the factory.

So summary of the testing and all is on the sound settings menu shot at post #1, right? I don't find the bass overbearing at all but I'll try that setting nevertheless.

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The sound was unlistenable to me because I am long accustomed to "flat" tonal balance, including throughout the bass. As I said, I discovered this in a dealer parking lot when I began shopping for a 2019 GT. (Once the bass is flat respective to the rest of the spectrum, the listener can easily follow any aspect of the music, including the bass player. The bass no longer "drowns out" the rest of the music.)

I was prepared to go full monty by ordering a Parts Express 10" DVC woofer, and either retrofitting it into the factory box, or else buy a Zenclosures box. I have the means to test for and design the optimum box size, sealed vs vented, etc.

Ultimately I determined (through rigorous scientific method, lol) that I could achieve the sound I wanted just by using the controls. So that is the good news! And others can try this adjustment for free after I put in the hours of effort.

try to disable the factory EQ with forescan, maybe that would be better for you. makes everything flat
that's all I did and I love it.

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Yes, I did consider and still am considering that option. I would have to slog through the long Forscan thread(s) and study up on that. Any direct pointing me to the relevant info is appreciated. Nevertheless, I wanted to checkout what was going on via my own acoustic methods first.

Yes, I understand. But does that one line just remove EQ from the subwoofer channels? What about the subwoofer overall gain? That is primarily what I want lowered.

Also, if EQ defeat takes out EQ from ALL the channels then that could be a problem Again, I'd have to know the voltage transfer function to every driver in the car before the defeat. It is possible that Ford/B&O compensated out cone breakups, and other non-flat anomalies in the drivers' responses. Something that I would not want eliminated!